1. Field of the Invention
The present invention relates to an automatic transport system for transporting articles by an automatic transport vehicle at an assembly location in a plant and the like without human attendance, and particularly to an automatic transport system which detects by a sensor an obstruction located ahead of the automatic transport vehicle in its moving direction to control the operation of the automatic transport vehicle.
2. Description of Related Art
Automatic transport vehicles (hereinafter referred to as vehicles) are advantageously used in transporting parts in an assembly process in a plant and the like. Particularly, in a manufacturing semiconductor process, vehicles are used in transferring and assembling semiconductor wafers in the clean room without human intervention for preventing the contamination with dust and the like. For example, an Overhead Hoist Transport vehicle (hereinafter referred to as xe2x80x9cOHT vehiclexe2x80x9d), which travels along a ceiling rail in the clean room is used in the assembly process of semiconductor wafers and the liquid crystal devices.
Moreover, an optical beam reflection sensor (hereinafter referred to as xe2x80x9coptical sensorxe2x80x9d) such as an infrared type sensor, serving as a non-contact obstruction detecting apparatus of vehicles. The optical sensor detects an obstruction ahead in the moving direction by emitting an optical beam which is conical-shaped. If a long range detection sensor is provided at the front of the vehicle as a front detection sensor, the vehicle is stopped when the long range detection sensor is triggered while it is traveling. If a vehicle has two front detection sensor as a front detection sensor, detection may be carried out in two steps by two front detection sensors.
FIG. 9 is an operation conceptual view of an OHT system used in the semiconductor wafer manufacturing process or the like. The right portion of FIG. 9 is a side view of an OHT vehicle and the left portion of FIG. 9 is a view showing a projection of the OHT vehicle ahead in the moving direction at a predetermined position in the moving direction.
In FIG. 9, a rail 21 is laid down on a ceiling of a clean room (not shown) along the process line, and a part of the rail 21 is shown therein. An OHT vehicle 22 movably hangs on a lower portion of the rail 21. For example, the OHT vehicle 22 is constituted such that it has a box-like frame and can hold a wafer cassette 23 in this frame and runs along the rail 21.
Moreover, a front detection sensor 24 is attached to the front portion of the OHP vehicle 22 in the moving direction. As the front detection sensor 24, an optical sensor of such as an infrared sensor is generally used such that an obstruction in the moving direction of the OHT vehicle 22 can be detected in a non-contact state. In other words, an obstruction ahead is detected by optical beams emitted in a conical shape from the front detection sensor 24. Then, when the front detection sensor 24 detects the obstruction ahead, the OHT vehicle 22 is designed to automatically stop.
Additionally, in FIG. 9, although the front detection sensor 24 at the left side surface of the OHT vehicle 22 is provided for movement to the left side of the figure, the OHT vehicle 22 normally moves in two directions. In such a case, the front detection sensor 24 IS also provided at the right side surface of the OHT vehicle 22.
However, in some cases, an associated manufacturing apparatus may be present very close to the periphery of the rail 21, the door of the manufacturing apparatus may be opened, or parts being processed are located close to the periphery of the rail 21. Further, in other cases, in locations outside of the passage of the OHT vehicle 22, there may be a stepladder, a workbench or the like for maintenance, or a person. For this reason, in order to prevent the OHT vehicle 22 from colliding with them, the front detection sensor 24 on the OHT vehicle 22 detect obstructions ahead. However, as shown in FIG. 9, if the detection area of light emitted from the front detection sensor 24 is widened as shown in a detection area A in order to detect obstructions located in the passage area of the OHT vehicle 22, there is a possibility that objects which are at the periphery of the running path will unnecessarily be detected and that the OHT vehicle 22 will not run.
In other words, the left side of the drawing indicates the passage area C of the OHT vehicle 22, as seen from the front of the OHT vehicle 22 in the moving direction, by a solid line. Also, a wide detection area A where the entire passage area C of the OHT vehicle 22 can be detected is indicated by a broken line. This large detection area A is the bottom surface of the cone of the light beam emitted by the front detection sensor 24 at a predetermined position.
Unlike the wide circular detection area A that is the bottom of a conical surface, if the front shape of the OHT vehicle 22 that is the passage area C of the OHT vehicle 22 is rectangular, for example, as illustrated in the figure, excess detection area D, in which the wide detection area A lies outside of the passage area C to be detected will occur. If an object is located in this excess detection area D, the OHT vehicle 22 will stopped even though the object is not actually obstructing the passage of the OHT vehicle 22.
On the other hand, if the detection area is narrowed as in the narrow detection area B indicated by a broken line, the corner portions of the passage area C of the OHT vehicle 22 cannot be detected, and form a non-detection area E. In such a case, there is the concern that the OHT vehicle 22 will collide with an object in the non-detection area E which is in the corner portion of the vehicle, when the vehicle passes the object.
FIG. 10 is an explanatory view showing the front detection sensor of the OHT vehicle 22 and an example of an obstruction. As illustrated in this figure, a stepladder 25 is placed in front, in the moving direction, of the OHT vehicle 22. In this case, if the detection area at the front detection sensor 24 is wide, as in the wide detection area A, the stepladder 25 is detected as an obstruction and the OHT vehicle 22 is stopped even though the OHT vehicle 22 will not collide with the stepladder 25. Furthermore, if the detection area is narrowed as in the narrow detection area B, the stepladder 25 is not detected. However, if workpieses or the like are placed at a location very close to the OHT vehicle 22, there is the concern that the OHT vehicle 22 will collide with them and break them since they cannot be detected.
FIG. 11 is a conceptual view showing an OHT vehicle used in a semiconductor manufacturing apparatus. As illustrated in this figure, for example, in the apparatus for manufacturing a 300 mm wafer, a distance P between the end surface of the OHT vehicle 22 that transports the wafer and the front surface of the semiconductor manufacturing apparatus 26 is set to about 30 mm on the basis of a standard distance. It is assumed that working is carried out in such small distances. If the detection area is too wide, the front detection sensor 24 will detect the door of the semiconductor manufacturing apparatus 26, so that the OHT vehicle 22 will not operates well and workcannot be carried out. Moreover, if the detection area is narrowed, there is the concern that the corner of the OHT vehicle 22 will contact semiconductor wafers (not shown) mounted on the semiconductor manufacturing apparatus 26 and these semiconductor wafers will be broken.
FIG. 12 is a conceptual view showing a vehicle using two front detection sensors for long range and medium range detection. The vehicle 111 is provided with a medium range detection sensor (not shown) which can detect over a medium detection range 113 and a long range detection sensor (not shown) which can detect over a long detection range 112. The vehicle 111 detect an obstruction which is loaded ahead in moving direction by switching the respective sensors. Then, control is performed so that the speed of the vehicle 111 is reduced when the long range detection sensor works and makes a detection within the long detection range 112 and the vehicle 111 is stopped when the medium range detection sensor makes a detection in the medium detection range 113.
FIG. 13 is a conceptual view showing an example of the operation state of a plurality of vehicles in a general OHT system. This figure is a conceptual view to explain a system in which a transport apparatus comprising a plurality of vehicles operating between the assembly apparatuses such as a plurality of semiconductor manufacturing apparatuses. In this figure, a rail 124 is provided along a plurality of assembly apparatuses 121, 122, 123, and a plurality of vehicles 125 and 126 travel on the rail 124. Then, in the case of operating the transport apparatus comprising a plurality of vehicles 125 and 126 which detect an obstruction which is located ahead by the front detection sensor as shown in FIG. 12, described above, it is effective for the respective vehicles 125 and 126 to made to be as close as possible to the vehicle in front when stopping in order to increase the transport efficiency of the system.
The transport efficiency of the transport system largely differs depending on whether the trailing vehicle 126 can move to a position G or only to a position H when the front vehicle 125 is placed at a position F as shown in FIG. 13. For example, it is assumed that there are requests for transfer from transfer ports 127 at positions F and G simultaneously in the assembly apparatus 121. If the trailing vehicle 126 can move to the position G when the front vehicle 125 is stopped at the position F, the simultaneous transfer can be carried out at the positions F and G. However, if the trailing vehicle 126 can move to only the position H, the trailing vehicle 126 cannot move to the position G until the front vehicle 125 finishes transferring at the position F and leaves the position F. Therefore, the transfer efficiency of the trailing vehicle 126 at the position G is decreased.
On the other hand, the conventional use of the general front detection sensors is described below. Specifically, as explained in the FIG. 12, when the vehicle moves close to the obstruction, the long range detection sensor detects the obstruction located the long detection range 112, firstly. Next, the sensor is changed to the medium range detection sensor or the detection range of the long range detection sensor is shortened to carry out the detection of the obstruction in the medium detection range 113. In this way, the detection range of sensor is shortened in two steps, the speed of the vehicle 111 is reduced, and then the vehicle stops at a predetermined position. In order to stop a vehicle 111 moving at a high speed before colliding with an obstruction, it is necessary to allow for a braking distance to start braking. For this reason, the detection occur in two steps for the long detection range 112 and the medium detection range 113 in the operation control of the vehicle 111.
However, in this case as described above, the front vehicle, which is regarded as an obstruction, may move forwards and is no longer regarded as an obstruction in some cases. This results in unnecessary braking, which reduces the operation efficiency of the entire OHT system. There is a method of preventing the unnecessary braking, that is to reduce the moving speed of the vehicle and to shorten the braking distance. However, this results in a reduction in the operating speed, so that the operation efficiency of the entirety of the OHT system is reduced after all.
For this reason, in the general OHT system, the speed of the vehicle is reduced in the long detection range or the medium detection range based on the detection result of the long range detection sensor, and the vehicle is stopped in the short detection range, which is very close to the front vehicle. The switching between the long detection range and the medium detection range using the long range detection sensor is generally decided based on the size of the vehicle and the speed, or the degree of the speed reduction or the like and the switching is decided such that after the operation of the long range detection sensor, the speed reduction of the vehicle and the stopping thereof are completed before the trailing vehicle contacts the obstruction. For example, when executing long range detection, the vehicle is operated if the distance between the obstruction ahead and the vehicle is 2 to 3 m. When executing medium range detection, the vehicle continues to operate when the distance between the obstruction ahead and the vehicle is 0.5 to 1.5 m. When executing short range detection, which covers shorter distances than the above, the vehicle is stopped. In this way, the distance between the obstruction ahead and the vehicle is predetermined in each detective range
If the vehicle is moving at high speed, it is necessary to reduce the detection range as little as possible after switching the detection range to the medium detection range from the long distance detection in order to stop the vehicle safely by the short range detection sensor after the operation of the long range detection sensor. However, the reduction of the detection range is limited to the braking distance of the vehicle, so that the medium detection range cannot be shortened much.
In view of the foregoing, an objective of the present invention is to provide an automatic transport vehicle providing sensors that can detect an obstruction present an area through which the automatic transport vehicle passes without losing the operation efficiency of the transport system.
Moreover, in an automatic transport vehicle comprising a plurality of vehicles, it is determined whether or not an obstacle ahead is a vehicle, and when the obstruction ahead is a vehicle, the distance up to the vehicle is shortened and the trailing vehicle is stopped, which makes it possible to improve the operation efficiency of an OHT system.
In order to solve the above-described problems and attain the above described objectives, the present invention provides an automatic transport system for transporting articles, comprising a front detecting device which detects an obstruction in a non-contact state in an area through which an automatic-transport vehicle passes, and a projection surface of said automatic transport vehicle, and when said front detecting device detects the obstruction in said area, the running speed of said automatic transport vehicle is reduced or said automatic transport vehicle is stopped.
Since the front detecting device of the present invention detects an obstruction which is located only the vehicle pass area of the actual passage region of the automatic transport vehicle. Therefore, in this transport system, only an object which located in the vehicle pass area is detected, and parts or the like in a position very close to a vehicle, but which does not impede the running of the vehicle, are not detected. In an automatic transport system, which is used in the assembly process of a semiconductor manufacturing apparatus, it is necessary to transport the workpieces or the like in the extremely narrow range to run the automatic transport vehicle. For this reason, the use of the automatic transport system of the present invention further improves the work efficiency.
Moreover, according to the automatic transport system, in the above-described invention, said front detecting device is an optical sensor, which emits an optical beam so as to irradiate an entire outer periphery of a projection surface of said automatic transport vehicle, and said optical sensor detects an obstruction in said area. Then, only the outer periphery of the area where the automatic transport vehicle passes is irradiated with the optical beam to detect the reflected light of this optical beam, making it possible to easily carry out detection in only the passage area of the automatic transport vehicle.
Furthermore, according to the automatic transport system of the above-described invention, a plurality of said optical sensors are provided near the outer periphery of a front surface of said automatic: transport vehicle, said optical sensors respectively emit the optical beams that irradiate a area throughout an entire outer periphery of the projection surface of said automatic transport vehicle, and said optical beams are fan-shaped.
The plurality of optical sensors are provided near the outer periphery of a front surface of the automatic transport vehicle in the moving direction. Then, the entire outer periphery of the running area is irradiated in the shape of a strip with the optical beams emitted from the respective optical sensors. As a specific method, for example, in the case of the automatic transport vehicle whose front surface in the moving direction is rectangular, if the strip slits are provided along the respective sides of the rectangle and the optical beams are emitted from the interior of these slits in the shape of a fan, the entire corresponding side of the rectangle, which is equivalent to a passage area, is irradiated with the optical beams. Therefore, the strip irradiation areas of the respective sides are combined with one another, making it possible to irradiate the outer periphery of the entire vehicle moving area the shape of a strip with the optical beams.
Moreover, according to the automatic transport system in the above-described invention, wherein the area irradiated by said optical beams lies partially outside of the outer area of said projection surface. Then, it is desirable that a slight allowance be provided in the width of the detection area such that erroneous detection of obstacles and a miss of detection can be prevented by mechanical shifts occurring when the automatic transport vehicle moves.
Still further, according to the automatic transport system of the present invention, the automatic transport vehicles constituting the automatic transport system of earn invention as-described above can be used in precision work, such as in a semiconductor manufacturing apparatus, and it can be employed in an Automatic Guided Vehicle (hereinafter referred to as xe2x80x9cAGVxe2x80x9d) running on the floor, a Rail Guided Vehicle (hereinafter referred to as xe2x80x9cRGVxe2x80x9d) running on a rail on the floor, which transport materials, parts, products or the like in automated plants or the like, other than an OHT, which runs on a ceiling rail.
The automatic transport system of the present invention is an automatic transport system, which comprises a plurality of vehicles running on a rail. The vehicles detect obstructions ahead in the moving direction and whether or not the obstruction is an automatic transport vehicle that runs in the front, so as to perform running control. According to the automatic transport system of the present invention, the running control differs depending on whether the obstruction ahead is a vehicle, and if the obstruction ahead is the vehicle, the vehicle is moved forward as much as possible to improve the entire transportation efficiency. In addition, the rail to which the present invention refers is not limited to a rail whose running route is physically constrained and the like. For example, a running route that runs on the floor and the like are also included therein.
Furthermore, according to the automatic transport system of the present invention, in the above invention, each of said plurality of vehicles comprises front detecting device for detecting whether at least two kinds of obstructions are present ahead and obstruction determining device which determine whether the obstructions detected by the detecting of the front detecting device are vehicles running ahead, and running control of the vehicles is performed based on the detection result of the front detecting device and the identification result of the obstruction determining device.
According to the automatic transport system of the present invention identification of whether an obstruction ahead is not a vehicle or is a vehicle running ahead is correctly performed. Then, the stopping of the trailing vehicle or the effective forward movement are carried out based on the identification result. This makes it possible to further improve the productivity of the entire system as compared with the conventional OHT transport system. Thus, running control can be carried out so that obstacles located in an area through which the vehicle passes can be detected with more reliability without losing the transportation efficiency of the system.
Still further, according to the automatic transport system of the present invention, in the above-described invention, said front detecting device comprises a long range detection sensor which detects an obstruction located in a long range, and a short range detection sensor which detects an obstruction located in a short range, said obstruction determining device determines whether or not an obstruction ahead detected by said long range detection sensor is an automatic transport vehicle running ahead, and running control of said automatic transport vehicle is performed based on a detection result of said long range detection sensor, an determining result of said obstruction determining device, and detection result of said short range detection sensor.
According to the automatic transport system of the present invention, the long range detection sensor, which has a relatively long detection range, detects obstructions, and the obstruction determining device identifies whether the detected obstruction is a vehicle. Then, the short range detection sensor, which has a short detection range, performs the stopping of the vehicle and control of the speed reduction based on the identification result of whether or not the detected obstruction is a vehicle, and on the distance to the obstruction.
In addition, according to the automatic transport system of the present invention, in the above-described invention, when the long range detection sensor detects an obstruction and the obstruction determining device identifies that the obstruction detected by the long range detection sensor is a vehicle running ahead, the vehicle moves ahead until the short range detection sensor detects the vehicle, and when the short range detection sensor detects the vehicle, the vehicle is stopped.
Still further, when the long range detection sensor detects an obstruction and the obstruction determining device identifies that the obstruction detected by the long range detection sensor is not a vehicle running ahead, the vehicle is immediately stopped, or when the short range detection sensor detects the vehicle, the vehicle is stopped.
According to the automatic transport system of the present invention, different and detailed operation control is performed depending on whether the obstruction ahead is a vehicle. If the obstruction ahead is a vehicle, the forward movement is effectively performed to improve the operation efficiency. Moreover, if the obstruction ahead is not a vehicle, the trailing vehicle is stopped at a safe distance and can be set to a standby state. For example, when a worker is working on the transportation rail, the worker is not erroneously recognized as a vehicle even if the worker is detected as an obstruction. For this reason, the trailing vehicle can be promptly stopped as required by the operation, which is different from the forward movement of the vehicle. As a result, the vehicle waits at a distance without approaching the worker, and this makes it possible to ease any concern that the worker may feel if the vehicle approaches the worker.
Furthermore, according to the automatic transport system of the present invention, in the above-described invention, the obstruction determining device comprises a light emitting device, which is provided at a rear portion of a vehicle running ahead, and a light receiving device, which-is provided at a front portion of a trailing vehicle. Alternatively, the obstruction determining device may comprise a reflector, which is provided at a rear portion of the vehicle running ahead, and a reflection sensor for receiving a reflected light, which is provided at a front portion of a trailing vehicle.
Still further, according to the automatic transport system of the present invention, in the above-described invention, the front detecting device is a plurality of optical sensors, which are provided over a predetermined periphery at a front portion of the vehicle, and the obstruction determining device comprises a logic circuit for signals from the plurality of optical sensors.
According to the automatic transport system of the present invention, the plurality of optical sensors are arranged around a predetermined periphery near an outer peripheral of the front surface of the vehicle in the moving direction, that is the entire periphery. Then, the entire outer periphery of the vehicle moving area is irradiated in the shape of a strip with the optical beams emitted from the respective optical sensors. As a specific method, for example, in the case of a vehicle whose front surface in the moving direction is rectangular, if the strip slits are provided along the respective sides of the rectangle and fan-shaped optical beams are emitted from these slits, the entire corresponding side of the rectangle, serving as a passage area, is irradiated with the optical beams. Therefore, the strip irradiation areas of the respective sides are combined with one another, making it possible to irradiate the outer periphery of the entire vehicle moving area in the shape of a strip with the optical beams. Additionally, if a logical calculation based on the signals from the plurality of optical sensors, for example, a logical sum, is performed, it is possible to detect that the obstruction is the vehicle only when the obstruction ahead is the vehicle.
Still further, in an automatic transport system that comprises a plurality of vehicles according to the present invention, the vehicles can be used in an AGV, RGV, or the like other than an OHT, which runs on ceiling rails.
As explained above, according to the automatic transport system of the present invention, since the automatic transport vehicle detects only substantially the area though which the automatic transport vehicle moved, only actual obstructions will be detected, without fail. There is no concern that an object or a person, which do not actually impede the running of the apparatus, will be detected, or that art obstruction will not be detected, causing unnecessary stopping and damage of objects. Therefore, the automatic transport vehicle can be run safely and efficiently, so that a safe and efficient automatic production system can be constructed.
According to the automatic transport system of the present invention, an obstruction present at in the area though which the vehicle of the moving direction will pass can be detected with more reliability without losing the transportation efficiency of the system. Also, identification of whether a obstruction ahead is a vehicle running ahead or not is correctly performed. Then, stopping of the trailing vehicle and the effective forward movement are carried out based on the identification result. This makes it possible to further improve the productivity of the entire system as compared with a conventional OHT transport system. Moreover, when a worker is working on the transportation rail, the worker is not erroneously recognized as a vehicle even if the worker is detected as an obstruction. For this reason, the trailing vehicle can be promptly stopped as required by the operation, which is different from the forward movement of the vehicle. As a result, the vehicle waits at a distance without approaching the worker, and this makes it possible to ease any concern that the worker may feel if the vehicle approaches the worker.